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Interior of Ganymede

The diagram to the left shows a cutaway of the possible inside structure of Ganymede, based on recent measurements by the Galileo spacecraft. It shows a small core of metal, overlain with some rocky material, overlain still further with ice. Further measurements by Galileo suggest that, in addition, Ganymede may have a thin, salty-slushy layer near the surface, where electric currents are found. Ice cannot support electric current, but water can. (That is why people don’t put electric appliances into the bathtub!)

When the Galileo spacecraft flew by Ganymede, to everyone's surprise it measured a very strong magnetic field for the first time near any moon! This provides further evidence that Ganymede is not completely frozen, but has a warm iron core.

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Minerals are the building blocks of rocks. They are non-living, solid, and, like all matter, are made of atoms of elements. There are many different types of minerals and each type is made of particular...more

When the Galileo spacecraft flew by Ganymede, it found something that was a big surprise to everyone -- a very strong magnetic field. This is the first time a strong magnetic field had been found near...more

You may wonder how it is that scientists know what the inside of a planet is like. The interior of a moon or planet can be closely determined from spacecraft navigation data when a spacecraft passes by...more

The surface of Ganymede is halfway between that of Callisto and that of Europa. Portions of the crust are of ancient age, while other portions are relatively new. The little white dots shown in this image...more

There has been no icy volcanism on Ganymede, nor continental drift, but it does seem that there have been movements of the surface. Examination of the surface of Ganymede reveals many kinds of faulting....more

The Galileo spacecraft was launched on October 19, 1989. Galileo had two parts: an orbiter and a descent probe that parachuted into Jupiter's atmosphere. Galileo's main mission was to explore Jupiter and...more

The Galileo spacecraft has finally reached the end of its road. Galileo has been orbiting Jupiter since 1995. On September 21, 2003, Galileo will dive into Jupiter's atmosphere and burn up. This crash...more